169 results on '"Meert, Joseph G."'
Search Results
152. Heat flow at the Platanares, Honduras, geothermal site
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Meert, Joseph G., primary and Smith, Douglas L., additional
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- 1991
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153. Reconstructions of the continents around the North Atlantic at about the 60th parallel
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Torsvik, Trond H., Van der Voo, Rob, Meert, Joseph G., Mosar, Jon, Walderhaug, Harald J., Torsvik, Trond H., Van der Voo, Rob, Meert, Joseph G., Mosar, Jon, and Walderhaug, Harald J.
- Abstract
Late Carboniferous–Early Tertiary apparent polar wander (APW) paths (300–40 Ma) for North America and Europe have been tested in various reconstructions. These paths demonstrate that the 500 fathom Bullard et al. fit is excellent from Late Carboniferous to Late Triassic times, but the continental configuration in northern Pangea changed systematically between the Late Triassic (ca. 214 Ma) and the Mid-Jurassic (ca. 170 Ma) due to pre-drift extension. Best fit North Atlantic reconstructions minimize differences in the Late Carboniferous–Early Jurassic and Late Cretaceous–Tertiary segments of the APW paths, but an enigmatic difference exists in the paths for most of the Jurassic, whereas for the Early Cretaceous the data from Europe are nearly non-existent. Greenland’s position is problematic in a Bullard et al. fit, because of a Late Triassic–Early Jurassic regime of compression (>300 km) that would be inherently required for the Norwegian Shelf and the Barents Sea, but which is geologically not defensible. We suggest a radically new fit for Greenland in between Europe and North America in the Early Mesozoic. This fit keeps Greenland ‘locked’ to Europe for the Late Paleozoic–Early Mesozoic and maintains a reconstruction that better complies with the offshore geological history of the Norwegian Shelf and the Barents Sea. Pre-drift (A24) extension amounted to approximately 450 km on the Mid-Norwegian Shelf but with peak extension in the Late Cretaceous.
154. Early Eocene high-flux magmatism and concurrent high-temperature metamorphism in the Gangdese belt, southern Tibet.
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Xuxuan Ma, Zhiqin Xu, Meert, Joseph G., Zuolin Tian, and Haibing Li
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MAGMATISM , *PETROLOGY , *PHASE equilibrium , *GEOCHEMISTRY , *CENOZOIC Era , *EOCENE Epoch , *GEOLOGICAL time scales - Abstract
The Himalayan-Tibetan orogen represents one of the major Cenozoic tectonic features on Earth, and yet considerable debate continues over the timing and sequence of collisional events leading to its formation. In this contribution, we present new field relations, petrology, geochemistry, geochronology, and phase equilibria modeling in the Gangdese belt of southern Tibet in an effort to address Indo-Asian collisional events in the region. These investigations reveal that the dominantly dioritic Nymo intrusive complex was formed at ca. 50-47 Ma. We establish that the Jurassic-aged Bima volcano-sedimentary sequence underwent early Eocene (50-47 Ma) high-temperature (HT) amphibolite-facies metamorphism. Petrology and phase equilibria modeling of garnet-biotite schists in the Bima rocks reveals mineral assemblages of melt + plagioclase + garnet + biotite + magnetite + ilmenite + sillimanite formed under conditions of 5.3-7.5 kbar and 700-800 °C. We contend that the early Eocene Nymo intrusive complex represents part of the ca. 50 Ma high-flux magmatic "flare-up" that triggered the HT amphibolite-facies metamorphism within the overlying plate during Indo-Asian collision. The synchroneity of high-flux magmatism and HT metamorphism in the Gangdese belt roughly coincided with the continuing Indo-Asian collisional process, implying the early Eocene closure of the Neotethys Ocean along the southern margin of the Lhasa terrane. [ABSTRACT FROM AUTHOR]
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- 2021
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155. A true polar wander trigger for the Great Jurassic East Asian Aridification.
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Zhiyu Yi, Yongqing Liu, and Meert, Joseph G.
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POLAR wandering , *PALEOMAGNETISM , *ARID regions , *VOLCANIC ash, tuff, etc. , *BIOTIC communities - Abstract
A drastic environmental change occurred during the Middle to Late Jurassic as much of East Asia transitioned from a wet seasonal to an extremely arid climate. The timing, scope, and especially mechanism for this aridification are contentious. In this study, we report paleomagnetic data and ages from Jurassic volcanic rocks in North China and for the first time reveal a large-scale southward displacement of ~25° for the Eastern Asian blocks (EABs) sometime between 174 ± 6 Ma and 157 ± 4 Ma. We suggest that the rapid motion documented by our paleomagnetic studies resulted from large-scale true polar wander (TPW). The TPW rotation displaced the EABs from the Northern Hemisphere humid-temperate belt into the subtropical/tropical arid zone. The resultant latitudinal motion coincided with a remarkable environmental change recorded over 10,000,000 km2 in East Asia between ca. 165 Ma and 155 Ma. We call the climate transition the "Great Jurassic East Asian Aridification" and argue that TPW-induced climatic shifts were also responsible for the demise of the Yanliao Biota and subsequent radiation of the Jehol Biota during the Late Jurassic and Early Cretaceous. [ABSTRACT FROM AUTHOR]
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- 2019
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156. The Story of Earth: The First 4.5 Billion Years, from Stardust to Living Planet.
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Meert, Joseph G.
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EARTH history ,NONFICTION - Abstract
The article reviews the book "The Story of Earth: The First 4.5 Billion Years, From Stardust to Living Planet" by Robert M. Hazen.
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- 2013
157. Paleomagnetic investigation of the Neoproterozoic Gagwe lavas and Mbozi complex, Tanzania and the assembly of Gondwana
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Meert, Joseph G., van der Voo, Rob, and Ayub, Samwel
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- 1995
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158. A note on the impact factor of Gondwana Research
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Meert, Joseph G.
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- 2003
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159. Neoproterozoic tectonic transition from subduction-related convergence to continental extension of the Tarim Block, NW China.
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Cai, Zhihui, He, Bizhu, Meert, Joseph G., Ma, Xuxuan, Jiao, Cunli, Liu, Ruohan, Chen, Xijie, and Yun, Xiaorui
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RARE earth metals , *MAFIC rocks , *SYENITE , *GEOLOGICAL time scales , *LITHOSPHERE - Abstract
• ~840 Ma rhyolitic clast and ~755 Ma syenite are reported in Aksu region. • The Late Neoproterozoic–Early Cambrian mafic rocks in the Aksu region can be divided into three phases. • Transition from subduction-related convergence to continental extension occurred around 760 Ma in NW Tarim. The Tarim Block, one of the three largest cratons in China, plays an important role in the reconstruction of the Rodinia supercontinent. Knowledge of the Neoproterozoic tectonic evolution of the Tarim Block, especially the tectonic transition from convergence to rifting, remains unclear. The Aksu terrane, an integral part of the Tarim Block, is marked by the occurrence of Neoproterozoic blueschists, conglomerates, and mafic rocks that may provide important constraints on its tectonic history. We present an integrated study involving detailed field observations, whole-rock geochemistry, and zircon U-Pb geochronology for rhyolitic clasts in a Neoproterozoic conglomerate, a syenite pluton and mafic rocks in the Aksu region. Zircon U-Pb dating of the rhyolite yielded a crystallization age of 840 ± 4 Ma. Geochemically, the rhyolite is characterized by enrichment of light rare earth elements and depletion of high field strength elements, indicating a subduction-related arc setting. Syenites interspersed with mafic intrusions were crystallized at ~755 Ma, representing fractional crystallization products from intra-plate mantle-derived basaltic magma. Based on a compilation of previous studies, we find that the Late Neoproterozoic–Early Cambrian mafic rocks in the Aksu region can be divided into three phases. Phase I mafic intrusions (~760–745 Ma) occurring as dikes intruded into the blueschist-bearing Aksu Group. Phase II mafic intrusions (~755 Ma) intruded into the Neoproterozoic Qiaoenbulake Formation. Phase III mafic rocks (~520 Ma) are sills or basalts hosted within the Sugaitebulake Formation. Detailed studies suggest that subduction of oceanic lithosphere in the Aksu area persisted until at least ~840 Ma. The transition from ocean-continent subduction to continental extension took place around ca. 760 Ma. At 755 Ma, the northwestern Tarim region experienced significant extension. [ABSTRACT FROM AUTHOR]
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- 2021
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160. Quantifying the Extent of the Paleo‐Asian Ocean During the Late Carboniferous to Early Permian.
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Zhang, Donghai, Huang, Baochun, Zhao, Guochun, Meert, Joseph G., Williams, Simon, Zhao, Jie, and Zhou, Tinghong
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OCEAN , *VOLCANIC ash, tuff, etc. , *OROGENIC belts , *REMANENCE ,PANGAEA (Supercontinent) - Abstract
Dating the closure of the Paleo‐Asian Ocean (PAO) is critical to our understanding of East Asian tectonics during the formation of Pangea, yet existing estimates differ by up to 130 Myr (380–250 Ma). We report two robust paleomagnetic results from 320 to 280 Ma volcanic strata in the South Mongolia‐Xing'an Belt. Stable characteristic remanences of both results are likely primary and characterized by positive fold tests, consistent polarity with the Kiaman Superchron (∼318–262 Ma) and average paleosecular variation. The new results indicate that the northward motion of North China and Mongolia paralleled Laurussia from the Late Carboniferous to Early Permian. The N‐S width of the PAO in the east‐central segment (reference site: 43°N/114°E) was ca. 2,700 km during the Late Carboniferous to Early Permian. This wide ocean impeded floral and faunal exchange until the Guadalupian, prior to its final closure by ca. 250 Ma. Plain Language Summary: The Paleo‐Asian Ocean (PAO) separated North China and Tarim from Mongolia and Siberia. The closure timing is contentious and ranges from the Late Devonian to Early Triassic, resulting in great uncertainty when trying to reconstruct the Asian blocks in Pangea. Volcanic rocks are ideal recorders of paleomagnetic signals and therefore sought after to provide rigid paleogeographic reconstructions. In this study, we present paleomagnetic constraints on the paleolatitudes of blocks from the northern and southern sides of the PAO and propose a ca. 2700‐kilometer ocean of this segment of the PAO during 308–290 Ma. The existence of this wide oceanic basin impeded floral and faunal interchange between North China and Mongolia. The PAO finally closed and formed a unified North China‐Amuria block at ca. 250 Ma. Key Points: Mongolia was situated at 34.0°N during 320–296 Ma and 43.6°N during 300–280 MaThe N‐S width of the Paleo‐Asian Ocean (PAO) in the east‐central segment was ca. 2,700 km during the Late Carboniferous to Early PermianThe PAO impeded floral and faunal interchange until the Guadalupian, prior to its closure at ca. 250 Ma [ABSTRACT FROM AUTHOR]
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- 2021
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161. Crystal accumulation induced Sr/Y variation: Insights from a rear-arc pluton in the western Central Qilian Belt, NW China.
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Li, Xue, Wang, Chao, Wu, Mei-yun, Zhang, Ji-heng, Zhu, Xiao-hui, Meert, Joseph G., Sun, Xiao-kui, Li, Hang, Hao, Jiang-bo, and Yu, Zun-pu
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TONALITE , *IGNEOUS intrusions , *PLAGIOCLASE , *CRYSTALS , *GEOLOGICAL time scales , *GEOCHEMISTRY , *APATITE , *GARNET - Abstract
[Display omitted] • Sr/Y ratios are formed by fractional crystallization. • Crystal-melt segregation is a major factor that controls the compositional variations of granites. Granitic plutons are interpreted as either the product of melts, cumulates or crystal-rich mush. The different hypotheses yield distinct interpretations on the diversity of geochemical compositions, particularly the high Sr/Y ratio, including melting of lower continental crust or a young subducting oceanic crust, fractionation of garnet at high pressure in the lower crust or upper mantle, and in-situ crystal-melt separation within the middle to upper crust. Here, we carried out detailed field and petrographic observations, geochronology, geochemistry, and isotopic studies of the Wulanyaodong pluton (WP) in the western Central Qilian belt to address these issues. The WP is composed of granodiorite, quartz diorite, syenogranite, monzogranite, felsic vein/dyke and microgranular enclaves that formed between 474 and 460 Ma. Pressure estimates suggest that the granodioritic and granitic units of the WP represent a magma evolution in the upper crust that formed between 14.1 and 1.0 km in depths and reflects a change in the architecture of the crustal magma system that was emplaced incrementally. Petrographic observation and geochemical analyses suggest that the granodiorites at WP with different Sr/Y ratios are likely to be the products of a magma mush with different degrees of plagioclase ± amphibole ± apatite accumulation, indicating crystal-melt separation processes. The microgranular enclaves and granite units represent late mafic magma injection, rejuvenation of granodioritic mush, and extracted melts, respectively. Rejuvenation of mush induced remobilization of residual melts to form small felsic veins and wide dykes that cross-cut the granodioritic unit. Our results highlight that crystal accumulation and melt segregation in the magma mush play a dominant role in triggering compositional variation in granite pluton. [ABSTRACT FROM AUTHOR]
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- 2023
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162. Grenville-age basement and early Paleozoic reworking in the Qilian Orogen, NW China: Implications for paleotectonic reconstruction of Rodinia and Gondwana.
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Li, Hang, Wang, Chao, Hames, Willis, Hao, Jiangbo, Meert, Joseph G., Yu, Zunpu, Zhang, Shuai, Sun, Xiaokui, Ma, Deqing, and Li, Xue
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OROGENIC belts , *PALEOZOIC Era , *CLASTIC rocks , *BASEMENTS , *SUTURE zones (Structural geology) , *ZIRCON analysis , *PROVENANCE (Geology) , *OROGENY ,GONDWANA (Continent) - Abstract
[Display omitted] • Grenville-age terrane is identified in the Qilian orogen. • The Precambrian basement of the Qilian orogen is divided into four distinct mega-sequences. • ∼475 Ma metamorphism was related to the subduction of the Proto-Tethys Ocean. The Qilian orogen at the northeastern margin of the Tibetan Plateau records a complete history from continental breakup to oceanic basin evolution and back to continental collision during the Neoproterozoic to Paleozoic interval. The Qilian Ocean, as a branch of the Proto-Tethys Ocean, was connected to the Iapetus Ocean but is lesser known than its two more famous counterparts. This paper presents zircon U-Pb and biotite-muscovite 40Ar/39Ar isotope data from the Yemananshan Complex in the western Central Qilian belt to assess the age and provenance of late Mesoproterozoic-early Paleozoic successions in the Qilian orogen. The results indicate the Central Qilian belt is characterized by Late Mesoproterozoic-early Neoproterozoic orogenesis with magmatism from 1200 Ma to 900 Ma and clastic metasedimentary rocks deposited between 1050 and 920 Ma. Statistical analysis of detrital zircon data and auxiliary temporal information from the Qilian orogen affirms the notion that sedimentation occurred in four distinct megasequences: (1) 1950–1850 Ma, the oldest known strata, (2) 1250–920 Ma, during Grenvillian-Sveconorwegian orogenesis, (3) 840–760 Ma, the disintegration of Rodinia, and (4) 650–550 Ma, which is typical of the orogenic belts that sutured the Gondwana continental blocks. Metamorphic zircon and 40Ar/39Ar isotope data indicate early Paleozoic metamorphism at ca. 475 Ma, which overlaps with magmatic activity associated with arc-back-arc basin development in the Central Qilian belt, which was associated with subduction of the Proto-Tethys in eastern Gondwana. [ABSTRACT FROM AUTHOR]
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- 2022
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163. Reappraisal of the petrogenetic processes of Neoproterozoic granitoids in the Altyn Tagh, NW China: Implications for reconstruction of the Qaidam block in Rodinia.
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Hao, Jiangbo, Wang, Chao, Liu, Liang, Wu, Hanning, Yang, Wenqiang, Kang, Lei, Gai, Yongsheng, Cao, Yuting, Meert, Joseph G., Ma, Deqing, Li, Hang, Yu, Zunpu, Sun, Xiaokui, and Zhang, Shuai
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ALUMINUM oxide , *MUSCOVITE ,RODINIA (Supercontinent) ,LAURENTIA (Continent) - Abstract
• The early Neoproterozoic granitoids in the Qaidam block show typical S-type properties, generating via partial melting of Mesoproterozoic metasedimentary rocks. • These granitoids were formed under high-temperature and low-pressure conditions in a late syn- to post-collision setting. • Qaidam block was located at the core of the Rodinia supercontinent, adjacent to Laurentia, Baltica and Amazonia during the Neoproterozoic. Neoproterozoic granitoids are widely distributed in the Altyn Tagh, and provide indispensable information on the pre-Cenozoic tectonics and evolutionary history at the northeastern margin of Tibetan Plateau. In this study, zircon U-Pb geochronological results show that the granitoids were emplaced during the interval between 997 Ma and 901 Ma. Petrological studies reveal that these granitoids have high Al 2 O 3 and K 2 O, low CaO and Na 2 O contents with Al-rich minerals, such as muscovite, which show typical S-type properties. These Neoproterozoic granitoids contain abundant inherited cores of Mesoproterozoic age with ε Hf (t) values between 9.43 to 4.60. We interpret this to indicate magma generation via partial melting of Mesoproterozoic metasedimentary rocks. Based on a comparison to similar Neoproterozoic magmatic and metamorphic events described in the East Kunlun and North Qaidam, we suggest that the Altyn Tagh, East Kunlun and North Qaidam were part of the same terrane (Qadiam block) during the early Neoproterozoic. Petrogenetic data when combined with other geological and tectonic information suggest a late syn- to post-collisional setting rather than a syn -collisional setting. The Qaidam block was probably located adjacent to Laurentia, Baltica and Amazonia, during Neoproterozoic time. [ABSTRACT FROM AUTHOR]
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- 2022
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164. The Paleoproterozoic magmatic–metamorphic events and cover sediments of the Tiekelik Belt and their tectonic implications for the southern margin of the Tarim Craton, northwestern China.
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Wang, Chao, Wang, Yong-He, Liu, Liang, He, Shi-Ping, Li, Rong-She, Li, Meng, Yang, Wen-Qiang, Cao, Yu-Ting, Meert, Joseph G., and Shi, Chao
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PROTEROZOIC Era , *METAMORPHIC rocks , *SEDIMENTS , *PLATE tectonics , *CRATONS , *ARCHAEAN - Abstract
The Tiekelik Belt in the southwestern part of the Tarim Craton, NW China, consists of Archean–Paleoproterozoic orthogneisses, and granitoids, and younger sedimentary successions. U–Pb dating of Paleoproterozoic rocks in the Tiekelik Belt has provided new information on the southwestern margin of the Tarim Craton. Two orthogneisses from the Heluositan Complex yielded crystallization ages in the interval 2310–2260 Ma and metamorphic ages of 2040–2007 Ma and 1830 Ma, respectively. Two syenogranites from the Buweituwei pluton yielded crystallization ages of 1900 and 1795 Ma. Detrital zircon analyses from sedimentary rocks nonconformably overlying the Buweituwei and Akazi plutons indicate maximum depositional ages between 1950 Ma and 1780 Ma. Major detrital inputs are from the basement in the region and form prominent peaks at 1900–1800 Ma and 2300–2200 Ma. Our new data, combined with previous results, allow us to summarize the Archean–Paleoproterozoic tectonic evolution of the Tiekelik Belt as follows: (1) Emplacement of Archean-aged TTG magmas during the 3.14–2.76 Ga interval; (2) A series of 2.41–2.26 Ga magmatic events that represent an important period of crustal reworking within the Tarim craton; (3) 2.03–1.80 Ga magmatic and metamorphic events that include the emplacement of a 1.9 Ga mafic dyke suite into the Heluositan Complex along with several episodes of intraplate magmatism. The late magmatic events are coeval with metamorphism and may support an orogenic extensional model for the Tiekelik Belt during the 1.9–1.8 Ga interval; (4) post-1.8 Ga subsidence and formation of a Changcheng sequence in the Tiekelik Belt. The Paleoproterozoic ages of major tectonothermal events within the Tiekelik, North Altyn–Dunhuang block and Alashan block are almost identical and it is argued that they were connected at that time as North China and Tarim were part of the larger Columbia supercontinent. [ABSTRACT FROM AUTHOR]
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- 2014
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165. Geochemical and geochronologic constraints for Paleozoic magmatism related to the orogenic collapse in the Qimantagh-South Altyn region, northwestern China.
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Chao Wang, Liang Liu, Pei-Xi Xiao, Yu-Ting Cao, Hui-Yang Yu, Meert, Joseph G., and Wen-Tian Liang
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GEOCHEMISTRY , *GEOLOGICAL time scales , *PALEOZOIC Era , *MAGMATISM , *OROGENIC belts - Abstract
Voluminous and discrete early Paleozoic bimodal magmatic suites are thought to be the result of post-collisional extension following the amalgamation of East Kunlun and Altyn Tagh. In this paper, four representative magmatic units were studied for their geochemical fingerprint in conjunction with geochronological studies. The 467-445 Ma Mangya mafic suite shows E-MORB type rare earth element (REE) patterns that are the result of asthenospheric interaction with a metasomatized subcontinental lithosphere. High-K calc-alkaline granodiorites, intruded at ca. 450 Ma, are characterized by high Mg#, the least fractionated REE pattern without an Eu anomaly, as well as high Sr and low Rb/Sr ratio. We interpret these geochemical signals to result from lower crustal melting of garnet amphibolite at pressures between 16 and 22 kbar. A 430-420 Ma A-type granite is interpreted to result from the melting of metaigneous rocks at middle to lower crustal depths. Lastly, a late magmatic pulse occurs between 400 and 380 Ma and is represented by the Alk granite. The Alk granite is interpreted to be a product of metapelite melts and is associated with a smaller volume of mafic melts. U-Pb zircon geochronology of Paleozoic igneous rocks of the Qimantagh-South Altyn reveals that most of the magmatic episodes are either coeval with, or post, extensional deformation. This phase of extension is supported by the exhumation of HP/UHP metamorphic rocks and crustal anatexis. Collectively, the evolutionary stages documented in this study correspond to a succession of post-collisional, postorogenic and, ultimately, within plate magmatic episodes. The overall features support orogenic collapse via removal of a thickened lithospheric root beneath the East Kunlun-Altyn Tagh collisional orogen during early Paleozoic. [ABSTRACT FROM AUTHOR]
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- 2014
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166. Phanerozoic polar wander, palaeogeography and dynamics
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Torsvik, Trond H., Van der Voo, Rob, Preeden, Ulla, Mac Niocaill, Conall, Steinberger, Bernhard, Doubrovine, Pavel V., van Hinsbergen, Douwe J.J., Domeier, Mathew, Gaina, Carmen, Tohver, Eric, Meert, Joseph G., McCausland, Phil J.A., and Cocks, L. Robin M.
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PHANEROZOIC Eon , *PALEOGEOGRAPHY , *POLAR wandering , *GEODYNAMICS , *PALEOZOIC stratigraphic geology , *GEOCHEMISTRY , *MESOZOIC paleomagnetism , *DATABASES ,GONDWANA (Continent) - Abstract
Abstract: A significant number of new palaeomagnetic poles have become available since the last time a compilation was made (assembled in 2005, published in 2008) to indicate to us that a new and significantly expanded set of tables with palaeomagnetic results would be valuable, with results coming from the Gondwana cratonic elements, Laurentia, Baltica/Europe, and Siberia. Following the Silurian Caledonian Orogeny, Laurentia''s and Baltica''s Apparent Polar Wander Paths (APWPs) can be merged into a Laurussia path, followed in turn by a merger of the Laurussia and Siberia data from latest Permian time onward into a Laurasian combined path. Meanwhile, after about 320Ma, Gondwana''s and Laurussia/Laurasia''s path can be combined into what comes steadily closer to the ideal of a Global Apparent Polar Wander Path (GAPWaP) for late Palaeozoic and younger times. Tests for True Polar Wander (TPW) episodes are now feasible since Pangaea fusion and we identify four important episodes of Mesozoic TPW between 250 and 100Ma. TPW rates are in the order of 0.45–0.8°/M.y. but cumulative TPW is nearly zero since the Late Carboniferous. With the exception of a few intervals where data are truly scarce (e.g., 390–340Ma), the palaeomagnetic database is robust and allows us to make a series of new palaeogeographic reconstructions from the Late Cambrian to the Palaeogene. [Copyright &y& Elsevier]
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- 2012
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167. Soft-sediment deformation structures (SSDS) in the Ediacaran and lower Cambrian succession of the Aksu area, NW Tarim Basin, and their implications.
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He, Bizhu, Jiao, Cunli, Cai, Zhihui, Liu, Ruohan, Meert, Joseph G., Yun, Xiaorui, Wang, Tianyu, Chen, Weiwei, Yu, Zhuoying, Li, Jinchang, Peng, Shoutao, Hao, Guangming, Guo, Xianpu, and Qiao, Xiufu
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SEDIMENTARY rocks , *DEFORMATIONS (Mechanics) , *PLASTIC extrusion , *MARINE sediments , *GAMMA rays , *BRECCIA ,GONDWANA (Continent) - Abstract
The Tarim Basin, the largest continental and marine superimposed basin in the northwestern part of China, is typically viewed as a stable and uninterrupted sequence during the Ediacaran-Cambrian transition. Undeformed strata, thick shallow marine sediments and thin deep marine sediments characterize the basin. In this study, we identify various types of soft-sediment deformation structures (SSDS) and an unconformity at four localities in the Aksu area, NW Tarim Basin. SSDSs include large-scale load structures, plastic intrusions and extrusions, load casts and pillow structures, liquefied breccias, ground fissures and lateral liquefaction, boudinage-like SSDSs, mound and sag structures, slumps, and small syn -sedimentary faults. The deformed layers are sandwiched between undeformed sedimentary rocks. Deformation features are found in the (a) lower Cambrian Yuertusi Formation consisting of interbedded thin black shale and phosphorite chert layers, thick-bedded shallow gray dolomite and silicate layers; (b) upper Ediacaran Qigebulak Formation composed of dark gray to gray dolomite and grayish green mudstone layers; (c) in the brown sandstone layers of the lower Ediacaran Sugaitebulak Formation. These units contain fluvial-lacustrine, nearshore, carbonate platform, shelf, and bathyal sedimentary environments. The SSDSs and more detailed stratigraphy indicate a dynamic setting that includes the heretofore unrecognized unconformities, a sub-stratigraphic sequence interface and high magnitude seismic events. The SSDS were produced during rifting, short sub-aerial exposure and frequent seismic disturbances. Combined on the carbon and oxygen isotope records, gamma radiations and the concentrations of main and trace elements, the differences between the SSDS layers and the undeformed layers are preliminary analyzed. We propose that this sequence not reflect a stable tectonic-sedimentary environment during the Ediacaran-Cambrian transition. Therefore, these units provide a unique glimpse into paleo-tectonic activity and paleo-ecological-environmental variation in the Tarim Basin during the late period of Rodinia breakup and the assembly of Gondwana. • Various soft-sediment deformation structures are recognized in Ediacaran-Cambrian. • Rift activity, transient exposure and post-rift subsidence with paleo-earthquakes. • Not a stable tectono-sedimentary environment during the E -C transition. • SSDSs provide a unique glimpse into the paleo-tectonic-environmental variations. • Respond to the activities of the late Rodinia break-up and the assembly of Gondwana. [ABSTRACT FROM AUTHOR]
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- 2021
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168. Intraoceanic back-arc magma diversity: Insights from a relic of the Proto-Tethys oceanic lithosphere in the western Qilian Orogen, NW China.
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Zhao, Guojun, Wang, Chao, Zhu, Xiaohui, Hao, Jiangbo, Li, Hang, Meert, Joseph G., Gai, Yongsheng, Long, Xiaoping, and Ma, Tuo
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LITHOSPHERE , *VOLCANIC ash, tuff, etc. , *MAGMAS , *ADAKITE , *BACK-arc basins , *SIDEROPHILE elements , *OCEANIC crust , *STRONTIUM ,GONDWANA (Continent) - Abstract
The Qilian orogeny formed by subduction of the proto-Tethyan ocean along the northern margin of Gondwana. In this paper we report geochemical, zircon U-Pb-Hf, and mapping data of the Duoruonuoer volcanic rocks from the western Qilian Orogen. Based on distinct geochemical compositions, four melt types can be distinguished: boninite-like basalt, OIB-like basalt, MORB, and high-K to shoshonitic volcanic rocks (HKSV). Field relationships show a compositional change from HKSV, MORB, OIB to boninite-like basalt, from north to south. The boninite-like basalt is low to medium-K calc-alkaline, with low TiO 2 (0.13–0.18 < 0.5 wt%) and high CaO/Al 2 O 3 ratio (0.72–0.80), similar to high-Ca back-arc boninite. The geochemical characteristics of Duoruonuoer OIB-like basalt, MORB, and HKSV are similar to those of the Izu-Bonin (IB) back-arc magmatic assemblages. Boninite-like basalt is enriched in LILEs, and has low Ce/Pb, and high Sr/Nd, Ba/Nb ratios, indicating an addition of a shallow subduction-derived fluid phase. Inferred pressures of magma segregation are 0.9–1.4 GPa with temperatures of 1200–1370 °C consistent with melting of a highly depleted, low pressure hydrous mantle source. The MORB-like rock formed by mixing of depleted mantle and a subduction component, and is identical to back-arc basin floor basalt (BABB). The HKSV, dated at 475 Ma, shares the characteristics with lava from the IB back-arc seamount chains (rear-arc). Their low Ce/Pb and high Th/Yb and Th/Nb ratios are compatible with contributions from melts of deep subducting sediment and oceanic crust. High pressure (1.8–2.0 GPa) may reflect sourcing from a mantle melt at the base of thickened arc crust. The OIB-like basalts have high TiO 2 , Zr/Yb, Nb/Yb and Ce/Pb ratios, suggesting an enriched component from partial melting of the asthenosphere. The high-Fe 8 and Ti 8 composition of the Duoruonuoer OIB-like basalt is produced by fractional melting, similar to a spreading ridge segment developed a deeper source. The variety of Duoruonuoer back-arc magmatism highlights the importance of changes to the melt source region linked to replenishment of the mantle wedge by material extracted from the subducting slab and influx of more fertile mantle material. It is also controlled by evolution of the mantle wedge over time in the building of the back-arc basin. These findings provide evidence for c.475 Ma back-arc basin developed on a thickened arc lithosphere at the western Qilian Orogen. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
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169. Geochemical characterization of a reconstructed 1110 Ma Large Igneous Province.
- Author
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Choudhary, Babita R., Ernst, Richard E., Xu, Yi-Gang, Evans, David A.D., de Kock, Michiel O., Meert, Joseph G., Ruiz, Amarildo S., and Lima, Gabrielle A.
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IGNEOUS provinces , *GEOCHEMISTRY , *DIKES (Geology) , *ZIRCON , *MAGMAS , *CRATONS , *PALEOMAGNETISM , *METASOMATISM - Abstract
• 1110 Ma units in four crustal blocks (Kalahari, Congo, India and Amazonia) are reconstructed as a single LIP in "Umkondia". • We compare the geochemistry for reconstructed 1110 Ma LIP regarding spatial distribution of studied dykes with respect to the plume centre. • Geochemistry divides into high and low Ti groups with a tendency for the high Ti group to be located more proximal to the plume centre. • The reconstruction is based on paleomagnetism and dyke swarm trends except for Amazonia which is only based on dyke trends. • Our model juxtaposed Amazonia against the western margin of the SF/Congo craton before 1110 Ma after separation of the Siberian craton at c. 1380 Ma. 1110 Ma Large Igneous Province (LIP) fragments in the Kalahari craton, southern Africa (Umkondo LIP); Dronning Maud Land, Antarctica; Bundelkhand portion of Indian craton (Mahoba dolerite dykes); Congo craton (Huila-Epembe dolerite dykes); and Amazonia (Rincon del Tigre-Huanchaca LIP) have been reconstructed as a single LIP with plume centre beneath the NW part of the Kalahari Craton. This paper offers the best estimates for the paleoposition of the Indian and Amazonian cratons along with conjoined Kalahari-SF/Congo reconstruction. This 1110 Ma mafic magmatism is dominantly tholeiitic, ranging from basalt to andesitic basalt in composition, generated over a range of mantle melting depths [(Gd/Yb)N = 1.2–2.3], exhibit low to high contamination with crustal components (negative Nb anomalies, eNd (0 to −12), and elevated Th/Yb). The data fall into two Groups based on TiO 2 content, with Group 1 (low Ti) of andesitic basalt composition, and Group 2 (high Ti) exhibiting a basaltic affinity. Group 1 magmas were generated in the spinel lherzolite field followed by significant contamination likely during passage through metasomatised lithospheric mantle in crustal magma chambers. A greater melting depth reaching into the garnet lherzolite field is proposed for the Group 2 magmas. The majority of Group 2 units are located in the Kalahari and Congo cratons, and this reflects onset of deeper melting closer to the interpreted plume axis in our reconstruction. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
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